The present invention concerns a watertight push button device, particularly for controlling a timepiece, said device comprising:
a body inside which an oblong cavity is arranged, PA1 a stem slidingly arranged in said cavity and connected to a push button head in order to move axially against the force of a return spring when a control push is applied to the push button head, and PA1 sealing means ensuring a watertight sealing of said cavity on the side of the push button head.
In the watchmaking field, conventional push button devices comprise a body which is generally termed a "push button tube", and inside which is arranged an open cavity having oblong shape. A stem is arranged in this cavity, called a push button stem, which extends longitudinally inside said body.
In most applications, this device also comprises a return spring which abuts firstly the base of said aforementioned body, and secondly a shoulder arranged on the stem.
Further, a push button head is driven onto a first end of the push button stem which projects out of the body, this stem comprising, at its second end, a screw which is intended to come into contact with a control member of the timepiece. This screw, under the action of the return spring, is brought to abut the base of the body, which prevents the movement of the push button stem beyond a certain limit during its return movement.
This type of device may be actuated very easily by the wearer of the timepiece to activate the corresponding control of this timepiece. However, it is known that these controls which are generally made up of mechanical components are very fragile since they are often made of metallic parts of small thickness, these metallic parts, which may be very complex, cooperating in turn with other mechanical components of the timepiece to assure the control of the required function.
It can thus be seen that brutal or too rapid actions applied to the push button device may seriously damage said control components, the timepiece being in such case inoperable and requiring repair by an expert watchmaker.
On the other hand, in conventional push buttons of timepieces such as chronographs, the return spring is precompressed relatively tightly in order to prevent the push button being accidentally actuated, for example if an obstacle or a part of the body of the wearer comes into contact with the push button head. Thus, as soon as the head is pushed with sufficient force to overcome that of the spring, the sliding movement of the stem is then achieved with a relatively small increase in the force to be applied. Consequently, an accidental push often leads to a full depression of the stem and unintentional activation of the corresponding function of the timepiece. If one wishes to avoid this disadvantage by increasing the initial force of the spring, normal manual actuation may become difficult. Furthermore the spring becomes too cumbersome.
Swiss patent No. 672 041 discloses a watertight push button device of the type specified above, in which the water resistance is assured by resilient metallic bellows fixed to the head and body of the push button. Due to its corrugated profile, the bellows act as a spring component complementing the conventional spring. However, this construction does not assist in avoiding the problems cited above.